The original Dead Rising featured a full set of Mega Man armor and a functional Mega Buster. Well, if Capcom's bringing back Frank West, why not bring back a Mega Man costume? So they did, with a twist.
This time you get Protoman armor, with a functioning arm cannon, of course. It takes some doing to assemble the suit, according to this GameFAQs user. You get the boots free; the shield and blaster are awarded for completing the game and getting the S ending. You gotta medal in all 30 challenges, save Jack and play poker with him, or defeat him in Sandbox mode.
Then you have to start another game with that save file—but not under New Game Plus. The blaster holds only 50 ammo.